Modulation Transfer Function (MTF) is one of the most important metrics for evaluating optical system performance, as it directly reflects resolution, contrast, and image fidelity. However, reliable and repeatable MTF results depend critically on proper laboratory setup.
Shape Optics Technologies Pte Ltd has designed and commissioned a professional MTF optical test laboratory in Singapore for fluorescence detection systems. In this article, we share practical setup guidelines, design considerations, and lessons learned to help you establish a robust MTF measurement environment.
Before configuring charts, cameras, and lighting, evaluate the following fundamentals:
Laboratory Environment Setup
To achieve precise MTF measurements, the test lab should be designed to minimize stray light and reflections.
Recommended Environment Conditions
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Use an interior, windowless room
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Walls painted neutral middle gray (N5) to black
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Paint finish: matte, flat, or eggshell
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Avoid:
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Polished metal surfaces
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White or light-colored objects
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Eliminate or cover:
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Room lights
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Windows
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Doorway light leakage
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LED indicators on equipment during testing
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These measures significantly reduce flare light, improving contrast accuracy in MTF measurements.
Test Chart Handling and Mounting
Proper Chart Handling
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Always wear clean white cotton gloves
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Avoid fingerprints, scratches, or bending
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Store charts in:
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Low heat
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Low humidity
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No direct sunlight
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Clear Acrylic Mounting for Transmissive Testing
For accurate and repeatable results:
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Use professionally mounted charts
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Mount charts on a smooth, flat acrylic board
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Ensure:
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No bubbles
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No warping
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No surface blemishes
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Precise chart mounting prevents local contrast loss that directly degrades MTF results.
Chart and Camera Alignment
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Chart and camera must be level relative to each other
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The chart does not need to be level with the ground
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Acceptable configurations include:
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Horizontal camera with vertical chart
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Camera pointing downward (e.g. microscope testing)
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Chart placed on a table or floor
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The key requirement is mutual orthogonality, not gravity alignment.
Optical Test Lab Equipment
Shape Optics recommends a modular MTF lab configuration as shown below:
Lighting Setup for MTF Measurement
Lighting Geometry
To achieve even, glare-free illumination:
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Position lights at 35°–45° relative to the chart
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Avoid:
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Lighting behind the lens
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Angles >45° (causes glare and shadows)
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Angles <20° (causes non-uniformity and texture artifacts)
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Use light modifiers (diffusers, barn doors) to suppress stray reflections.
Fixture Orientation
- Mount reflective light fixtures vertically
- This helps maintain consistent illumination from bottom to top of the chart
For detailed lighting arrange information, check the digraph as below:
Managing and Reducing Glare
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Matte charts are strongly recommended
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Semigloss charts are prone to:
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Edge glare
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Patch contamination
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If semigloss charts must be used:
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Reduce light-to-chart angle
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Re-check illumination uniformity after adjustment
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Glare in outer chart regions can invalidate MTF results, especially at high spatial frequencies.
Lighting Uniformity Requirements
Lighting uniformity is a critical requirement for accurate MTF testing.
How to Check Uniformity
- Divide the chart into a grid
- Measure illuminance at center, corners, edges, key chart features
Uniformity Targets
- ≤ 20% variation: Acceptable for SFR / MTF / distortion measurements
- ≤ ±5% variation: Required for tonal accuracy, color measurements, quantitative fluorescence analysis
Uniform lighting ensures that contrast variation originates from optics, not illumination.
References